Is HAL_UARTEx_RxEventCallback Size parameter calculated programmatically or by hardware

Question

I'm realizing UART-DMA with STM_HAL library and I want to know if message size is counted by hardware (counting clock ticks till line is idle for example) or by some program method(something like strlen). So if Size in

HAL_UARTEx_RxEventCallback(UART_HandleTypeDef *huart, uint16_t Size) 

is counted by hardware, I can send data in pure HEX format, but if it is calculated by something like strline, I may recieve problems if data is 0x00 and have to send data in ASCII.

I've tried to make some research in generated code in Keil but failed (maybe I didn't try hard enough) so maybe somebody can help me.

Answer 1

If you are using UART DMA, it is calculated by hardware.

If you check the call hierarchy of HAL_UARTEx_RxEventCallback using your ide, you can see how the Size variable is calculated.

The function is executed in the following flow.(Depending on the version of HAL Driver, it may be slightly different)

1. UART Idle Interrupt occur
2. Call HAL_UART_IRQHandler()
3. If DMA mod is enabled, Call HAL_UARTEx_RxEventCallback(huart, (huart->RxXferSize - huart->RxXferCount))

Therefore, Size variable is calculated as (huart->RxXferSize - huart->RxXferCount)

• huart->RxXferSize is a set value when initializing RX DMA.
• huart->RxXferCount is (huart->hdmarx)->Instance->NDTR

NDTR is a value calculated by hardware as the size of the buffer remaining after DMA transfer data to memory!!